Title :
Capacitive Sensing of Antenna Loading With an R–C Voltage Divider in a Tunable Antenna
Author :
Huttunen, Arttu ; Berg, Markus ; Myllymaki, S. ; Jantunen, H. ; Salonen, Erkki T.
Author_Institution :
Microelectron. & Mater. Phys. Labs., Univ. of Oulu, Oulu, Finland
Abstract :
This paper presents a capacitive sensor for antenna applications. The sensor is based on measuring voltage in a voltage divider made of a resistor and a capacitor formed in an antenna structure. The purpose of the device is to detect when the user of a mobile device holds a finger near the antenna element and allow triggering of compensation measures to regain antenna performance. A planar monopole antenna with an impedance tuning element was constructed for this purpose, and measurements showed that 10% of lost total efficiency can be regained by applying retuning. The sensor can measure capacitance changes of 5 fF and detect a human finger at up to a distance of 1 cm. Some design issues and caveats are also discussed.
Keywords :
capacitance measurement; capacitive sensors; capacitors; impedance matching; mobile handsets; monopole antennas; object detection; planar antennas; resistors; voltage dividers; R-C voltage divider; antenna element; antenna loading; capacitance measurement; capacitive sensor; capacitor; human finger detection; impedance tuning element; mobile device; planar monopole antenna; resistor; triggering; tunable antenna; voltage measurement; Antenna measurements; Antennas; Capacitance; Impedance; Thumb; Voltage measurement; Capacitance measurement; capacitive sensors; impedance matching; mobile antennas; parasitic capacitance;
Journal_Title :
Sensors Journal, IEEE
DOI :
10.1109/JSEN.2012.2223458
